Thermal dehydration of bitumen froth

ABSTRACT

BITUMEN FORTH CONTAINING WATER IS CONTACTED WITH HOT DRY BUTIMEN IN A MIXER TO VAPORIZE ALL THE WATER, THE THE MIXTURE IS FLASHED TO REMOVE THE WATER VAPOR AND PRODUCE DRY BITUMEN. PART OF THIS LATTER PRODUCT IS HEATED AND RECYCLED TO THE MIXER.

March 5 LUPUL THERMAL DEHYDRATION OF BITUMEN FROTH I Filed Jan. 15, 1973BITUMEN FROTH CONTAINING WATER WATER HOT BITUMEN b MIXER FLASH HEATERDRUM RECYCLED BITUMEN i DRY I BITUMEN PRODUCT United States PatentTHERMAL DEHYDRA IION OF BITUMEN FROTH Silver Lupul, Sherwood Park,Alberta, Canada, assignor to Canada-Cities Service, Ltd., Imperial OilLimited,

Aflantic Richfield Canada, Ltd., and Gulf Oil Canada Limited, fractionalpart interest to each Filed Jan. 15, 1973, Ser. No. 323,454 Int. Cl.C10c 3/00 US. Cl. 208-39 5 Claims ABSTRACT OF THE DISCLOSURE Bitumenfroth containing water is contacted with hot dry bitumen in a mixer tovaporize all the water. The mixture is flashed to remove the water vaporand produce dry bitumen. Part of this latter product is heated andrecycled to the mixer.

BACKGROUND OF THE INVENTION This invention relates to a process forthermally dehydrating bitumen froth. It finds application as one of theoperations in the combination of operations by which bitumen isextracted from tar sand.

A large proportion of the worlds known hydrocarbon reserves exists inthe form of tar sand. One large deposit of this material is found alongthe banks of the Athabasca River in Alberta. The tar sand compriseswater-Wet grains of sand sheathed in films of bitumen. In treating thetar sand to recover commercially saleable products, it is firstnecessary to separate the bitumen from the water and sand.

The extraction method commonly applied is known as the hot water method.In board outline, this method involves contacting the tar sand in atumbler with hot water and steam. The Water is supplied at a temperatureof about 180 F. and in a amount suflicient to produce a slurrycontaining about 20 to 25% by weight water. The steam is supplied in anamount sufficient to ensure that the slurry temperature is about 180 F.During slurrying, the bitumen films are ruptured and a preliminaryseparation of the sand grains and bitumen flecks takes place. At thesame time, air bubbles are entrained in the slurry. More hot water isadded to the slurry after it leaves the tumbler--typical1y this mightraise the slurry water content to about 50%. The diluted slurry is thenintroduced into a separator cell containing a body of hot water. Thecontents of the cell are commonly maintained at about 180 F. In thecell, the bitumen particles, which have become attached to air bubbles,tend to rise to the surface of the water body and form an oily primaryfroth. This froth is recovered in a launder running around the rim ofthe cell. The coarse sand particles tend to sink to the bottom of thecell and are drawn oif as tailings. A middlings stream, comprisingwater, fine solids (minus 325 mesh) and some bitumen, is continuouslywithdrawn from the cell at a point intermediate its ends. This middlingsstream is treated in a sub-aerated flotation cell to recover thecontained bitumen in the form of secondary froth. The primary andsecondary froths are combined and transferred into a holding tank toremove some of the contained solids and water by gravity settling.

All of the previously described process is extensively described in theliterature and does not form part of the present invention. However, itdoes produce the feed stock, bitumen froth containing solids and water,which is treated in accordance with this process. While the compositionof the froth can vary, it typically comprises 30% by weight water,solids and 60% bitumen.

Before the bitumen in the froth can be treated to recover salableproducts, it is necessary to remove most of ice the water. This has beendone by diluting the froth with naphtha and centrifuging the product toremove the water. However, this prior art system involves expensive,highwear equipment. Alternatively, the froth has been heated indirectlyin an exchanger with steam to vaporize the water; the Water vapor wassubsequently flashed off. How ever, this process was not pursued, mainlybecause of the ioullilng of the exchanger tubes by clay left behind bythe rot SUMMARY OF THE INVENTION The present invention is concerned withthat type of thermal dehydration process wherein the bitumen froth isheated, to vaporize contained water, and is then flashed to separate thewater vapor from the bitumen. The process has been developed with theobjects of (l) avoiding the use of heat exchangers; (2) minimizingfoaming and keeping it within predictable limits; and (3) keepingequipment costs low.

In accordance with the invention, dry bitumen is used as the vehicle forheating the froth. The bitumen is preheated to at least 300 F.,preferably to a temperature in the range 600-700 F. It is mixed with thefroth in a co-current flow mixer. The bitumen temperature, the amount ofbitumen used, and the mixer residence time are selected having regard tothe requirement that the desired amount of vaporization must becompleted within the mixer. The mixer product is flashed in a flash zoneof sufiicient volume and reduced pressure to produce water 'as overheadproduct and dry or substantially dry bitumen as the bottom product.Pa-rt of this bottom product may be recycled to the pre-heating stepmentioned above.

The mixer itself may be a downflow vessel having staggered, verticallyspaced plates which blank off the vessel cross section to restrict theflow area to about 20%. Alternatively, the mixer may be of the cyclonetype, as was used in the example following hereinbelow.

The process is operated so that substantially all Water vaporization iscarried out in the mixer. This is achieved by maintaining thetemperature (Tm) of the mixer product stream about the same as thetemperature (Tf) of the flash vessel bitumen stream. Preferably thetemperature difference is maintained at less than 10 F. One way of doingthis involves feeding the hot dry bitumen to the mixer at a constantrate and temperature, monitoring Tm and T and manipulating the rate atwhich froth is admitted to the mixer to maintain Tm equal to Tf.

The process is characterized by several advantages. By heating drybitumen instead of froth, erosion of furnace tubes is reduced because oflower fluid velocities. The capital cost of the mixer and flash vesselis less than that of the equipment used in prior art processes. Bycarrying out vaporization in the mixer and maintaining Tm and T7 equal,it is found that the amount of foam generated in the flash vessel isreduced and its behaviour within the vessel is reasonably predictable;this latter characteristic permits one to select the smallest possibleflash vessel for a given feed stock and operating conditions. Finally,the bitumen product contains only a small amount of water and thiscontent is reasonably consistent over a prolonged period of operation.

Broadly stated, the invention comprises a thermal dehydration processfor treating bitumen froth containing water, which process comprises:(a) heating substantially dry bitumen to a temperature greater than 300F.; (b) mixing bitumen froth with a sufficient amount of the hot, drybitumen of step (a) for a sufficiently long period of time to vaporize apredetermined amount of the water contained in the froth; and (c)flashing the product mixture to separate substantially all the vaporizedwater from the bitumen.

3 DESCRIPTION OF THE DRAWING In the drawing, FIG. 1 is a flow diagramillustrating the steps of the process.

DESCRIPTION OF THE PREFERRED EMBODIMENT (b) mixing bitumen froth with asufiicient amount of the hot, dry bitumen from step (a) for asufiiciently long period of time to vaporize a pre-determined amount ofthe water contained in the froth; and

(c) flashing the product mixture to separate substantially all thevaporized water from the bitumen.

2. The process as set forth in claim 1 wherein: the addition of bitumenfroth to the mixing step is controlled to maintain the temperature ofthe product leaving the mixing step substantially equal to thetemperature of the men, was fed, together with a hot, dry bitumen streamcomprising /2% by weight water, solids and the blmmen Product from theflashmg P- balance bitumen, into a mixer 1. The relevant flow rates, APmcess separatlng Watfil' from bltumetl froth temperatures and analyseswere as follows for a run of Which Comprises! hours: (a) heatingsubstantially dry bitumen to a temperature I TABLE I Flow rates(lbs/hr.) Temperature, F. Analyses (percent water) Hot, dry Hot, dryBitumen Bitumen Froth bitumen Water Froth bitumen Mixture product WaterFroth product Water The mixer 1 comprised a series of six cyclonemixers. within the range 600 F. to 700 F.;

Each cyclone had a cylindrical top section, provided with (b)co-currently mixing bitumen froth with a sufficient a tangential inlet,and a conical bottom section. The top 5 amount of the hot, dry bitumenof step (a) for a section had a diameter of 4 inches and length of 6inches. sufficiently long period of time to vaporize substan- The bottomsection reduced over a length of 4 inches to tially all of the WaterContained in the froth;

an outlet diameter of 1 inch. The cyclones were connected (0) flashingthe product mixture in a flash zone of by 1 inch diameter pipe. Theinlet pressure to the first sufficient volume to permit of theSeparation of cyclone was 55 p.s.i. and the outlet pressure from thelast stanti'ally all the vaporized water from the bitumen cyclone was 15p.s.i. The temperature of the product whereby all Overhead Product ofWaterand a bottom stream was maintained t about 300 F product ofsubstantially dry bitumen are produced The mixture was fed directly intoa flash drum 2. This from the fl 20118; and vessel was cylindrical inshape and had an interior diar cycling part Of the bottom product toprovide meter of 8 inches and a length of 38 feet. Its feed inlet was ybitumen for p located 10 feet from its top. The drum 2 was operated toThe Process as Set forth in Claim 3 w e t e admaintain a fl id d th f bt 20 f t, a f di dition of one of the components mixed in the mixingstep gagement zone bo t 8 f et i l h, d a pressure f is controlled tomaintain the temperature of the product 4 p.s.i. The flow rates,temperatures and compositions of from p substantially equal to thetemperature of the the product streams from the drum are given in- TableI. bottom Product from p As shown in Table I, the process was operatedto main- The Process Set forth in Cla m 1 wherein: the tain the mixerproduct stream 'at the same temperature as bitumen froth and y bitumenare mixed the flash drum bottom product. This was done bymanipucurrhntlylating the rate of froth feed to the mixer 1. It wasfound References Cited that the levels of the various layers within thedrum 2 UNITED STATES PATENTS remained substantially constant under theseconditions.

Our work has shown that the process must be operated 2550432 4/1951Thompson 20811 with a recycle oil temperature between 300 F. and 7002,775,541 12/1956 Karl 208-187 F. to vaporize the water at an acceptablerate. Preferably, 3,208,930 9/1965 Andtassy it should be operatedbetween 600 F. and 700 F. Below 3,298,117 1/1967 9 600 F., the materialrecirculation rate becomes excessive; 7/1967 Blchard above 700 1cracking of the bitumen begins to occur. 3331765 7/1967 C'fmevan et208188 While the invention has been described in detail with 33388148/1967 P et 208 11 respect to a preferred embodiment, it will beunderstood 3466240 9/1969 Stemmetz 208-11 by those skilled in the artthat various changes and modi- 3489672 1/1970 Schulman et a1 208-11fications may be made without departing from the spirit 355698o 1/1971Clark et a1 208-187 and scope of the invention and it is intended tocover all 3684699 8/1972 Vermeulen et 208 188 suc;l1/hchanges andmodifications in the appended claims. DELBERT E GANTZ Primary Examinerat is claimed 1s. 1. A process for separating water from bitumen frothV. OKEEFE, Assistant Examiner which comprises:

(a) heating substantially dry bitumen to a temperature greater than 300E;

US. Cl. X.R. 208-11, 187, 188

